Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
Gaseous and particulate emissions, for example, sulphur dioxides, nitrogen oxides, metals, carbon dioxide and other volatile organic compounds, create air quality concerns due to their potential impact on environmental quality, human health and well-being. As a result, there has been increasing importance placed on monitoring, as well as reducing, such emission levels. Within the transport sector, difficulties have been encountered in policing exhaust gas emissions generated by vehicles.
Recent figures have shown that those responsible for excess particulate emissions, the “gross polluters”, are primarily heavy vehicles. Indeed, it has been suggested that in Australia about 10% of heavy vehicles contribute to as much as 80% of heavy vehicle pollution. It therefore follows that these heavy vehicles with high particulate emissions pose a threat to the environment and general air quality
Regimes currently in place for monitoring vehicles with unacceptable levels of particulate emissions often rely on trained observers monitoring vehicles over a statutorily imposed time period. Potentially infringing vehicles are pinpointed by these observers and picked up for further assessment and measurement. It will be appreciated that this technique is extremely subjective and may result in very few prosecutions.
Attempts have been made to provide more reliable systems for detecting smoky vehicles without requiring them to be stopped and connected to measuring apparatus. For example, remote vehicle emission sensors have been used to detect gross polluters in traffic streams. These systems are based on the absorption of an invisible infrared laser beam by polluting gases in exhaust plumes. Each gas absorbs the laser light at characteristic wavelengths thus allowing detection of the pollutant gas. A digital image of the offending vehicle is recorded after each measurement. Coupled to a number plate reader and a vehicle type classifier, these systems can identify polluter travel patterns, improve enforcement actions and of course, result in a cleaner environment. Examples of such systems include the ESP Accusan RSD 4000 system from Environmental Systems Products Holdings Inc of Connecticut.
However, the reliability of the above systems is questionable for a number of reasons, including the fact that instantaneous emissions may not be indicative of the average or usual amount of pollutants emitted by a vehicle.